1. Field of the Invention
This application relates to cables. More particularly, this application relates to network cable insulation.
2. Description of Related Art
Communications cables are broadly grouped into two arrangements, fiber optic cables and metal conductor cables, each of which has their own unique set of construction parameters that affect the quality of the communication signals carried therethrough.
Regarding metal conductor cables, one typical arrangement is the LAN (Local Area Network) cable that is usually constructed of four pairs of twisted insulated copper conductors encased within a jacket. Other larger cables may employ more pairs of conductors.
In this typical four pair LAN cable construction, in addition to the outer jacket, each of the eight primary conductors are individually coated with an insulation layer. Special designs for LAN cables may include a cross-filler for better NEXT (Near End Cross Talk) performance.
Aside from electrical performance considerations, there are certain mechanical performance tests that need to be met. One such crucial test is the NFPA 262 flame test, which is a standard method of testing for flame travel and smoke generation in wires and cables that may be installed in air-handling spaces such as budding ductwork.
In this context, FEP (fluorinated Ethylene Polymer) resin, thanks to its outstanding electrical and flame performance, is a typical material choice for the LAN cable application, for use in the primary conductor insulation. Other fire resistant materials such FRPVC (Flame Resistant PVC) are used for the outer jacket as the balance of ruggedness versus electrical considerations are different for the outer jacket than for the primary insulation.
With respect to the use of FEP on the primary insulation however, because FEP resin is expensive and the source of supply is limited, it is desirable to reducing or replace the FEP using alternative materials.
One such prior art example, U.S. Pat. No. 5,563,377 illustrates a LAN cable where the insulation on each of the four pairs of primary conductors made of four insulated dual layers pairs where a smaller amount of FEP resin covers the primary insulation layer made of an olefin based flame retardant formulation, thus reducing the amount of FEP required.